1. Field of the Invention
The present invention generally relates to packaging integrated circuits, and more particularly is concerned with a method for packaging integrated circuits on a continuous reel or supply.
2. Description of the Prior Art
Conventional bonding of an integrated circuit or semiconductor device to a desired substrate is a process wherein a fine electrically-conductive wire is individually bonded to each electrical contact or pad of the integrated circuit. Such bonding involves individual alignment of a wire to each pad, and for integrated circuits which have many pads, may require a great deal of time and thereby increase costs.
An improved method of bonding and packaging integrated circuits is known as tape automated bonding or "TAB". In this system, chips are bonded to a carrier tape to form a supply. The tapes are then stored on reels for use in automated operations in known manners. Generally, the carrier tapes range in width from 8 mm. to 70 mm. and are multi-layer structures. A typical tape is a two layer strata of polyimide bonded to copper. Desired patterns are stamped or etched in the tape to form a station on the tape for receiving a chip. The patterns include small, flat fingers or leads in the copper layer which fan out to wider leads. Undesired polyimide surrounding the leads is removed.
An integrated circuit or chip is positioned above the station so that the contacts are aligned with the small fingers or leads. In a single operation, pads are thermally bonded to their respective leads simultaneously. The bonding operation can involve as many leads and pads as desired, with all bonding being performed in one step. To enhance conductivity, the leads may be plated with gold or other suitable materials before bonding.
After bonding is completed, the chips remain attached to the tape by the bond between the contact points and the fingers. The fingers are connected to the leads, which in turn are connected to the uncut portions of the tape. At a desired time, the leads are cut and the chip is removed from the tape. The chip and the cut leads may then be connected to a desired substrate.
Chips bonded to a carrier tape by the TAB process as described above provide a reel of components that may be used in automated assembly operations. Such reels may be transported to desired locations for testing and assembly and the like. Utilization of a TAB system increases production and provides an economical and reliable means for assembling and bonding integrated circuits.
While a TAB process provides an improved chip assembly method, several problems may arise during its use that render a chip unsatisfactory. First, chips bonded to carrier tapes are unprotected and exposed. Accidents and spills may introduce foreign materials to the chip environment. Second, as the carrier tape is wound on a reel, the chips risk being damaged or torn from the tape by mechanical stresses. Third, bonded leads may be broken or pulled away from a chip. Fourth, transportation and handling of the reels may jar a chip from the tape.
Consequently, a need arises for improvements in packaging and protecting integrated circuits bonded to carrier tapes. Improvements are needed to overcome the shortcomings of known bonding systems and to ensure reliability of chips after they have been bonded to a tape.